The traditional methods used for bleaching paper pulps use oxidizing agents which are essentially chlorine, oxygen and derivatives thereof.
The bleaching of paper pulps is carried out by a delignification operation which is complementary to that carried out during the heat and chemical treatment to which the plant is subjected, which leads to the raw paper pulp. This operation consists in an oxidative degradation of the colored molecules, which are essentially formed of more or less recombined lignin fragments, and which form a deposit during cooking on the paper fibers and of the residual lignin present in the fibers after cooking.
Many books and documents describe these operations. Reference will be made, for example, for further information, to the book Chemical Pulping, J. Gullishen, TAPPI and Paper Oy publisher, p 1 to 145, 2000. (www.tappi.org)
Chlorine and its derivatives require considerable quantities of water, greater than 50 tons of water per ton of pulps. The polluted water should then be discharged into rivers.
The pollution, even with a chemical and biological treatment of the effluents before discharge, is considerable with chlorine and sodium hypochlorite, in particular because of the toxicity of the organochlorinated compounds generated.
The use of oxygen, ozone and peroxides of the hydrogen peroxide and peracid type provides a first solution as regards the pollution caused by chlorine and its derivatives.
These technologies are now known and are understood.
In the same manner, reference may be made, for further information, to the book Chemical Pulping, J. Gullishen, TAPPI and Paper Oy publisher, p 146 to 213, 2000. (www.tappi.org) where these technologies are widely described from very recent references.
The quantities of water used remain high and these methods all require more than two steps of bringing the paper pulp to be bleached into contact with chemical reagents.
Furthermore, it is difficult to control the reactivity of ozone and of hydrogen peroxide toward cellulose and polysaccharides, which causes degradation of the mechanical qualities of the paper pulps thus treated.
The number of steps of bringing the paper pulps to be bleached into contact with the quantity of water used and discharged into the environment are as many factors which penalize these technologies from the economic and ecological point of view.
There is another way of manufacturing these bleached paper pulps which is radically different from the conventional methods and which is carried out by oxidative degradation of the lignins which is performed on the initial plant material. These technologies generally use performic acid and/or peracetic acid generated by direct reaction with hydrogen peroxide, with or without a catalyst.
The studies by J. Sundquist and colleagues on this subject appeared in: Papper Och Trä p 88, 2, 1986; and are summarized in Chemical Pulping, J. Gullishen, TAPPI and Paper Oy publisher, p 421 to 425 (www.tappi.org), show that this type of pulps at mechanical qualities of a lower quality. Furthermore, when the peracids are directly used on the plant, the consumption of hydrogen peroxide and of peracids is very high, which economically condemns this type of method.